Contaminated water exists in ever increasing quantities. Some of these waters contain low levels of organic compounds such as 2,4-dinitrotoluene, 1,4-dioxane, ethylene glycol, trinitrotoluene, phenols, anilines and pentachlorophenol. These compounds are susceptible to oxidation and/or photooxidation processes. By such reactions, these organic compounds can be oxidized to carbon dioxide and water and, in the case of nitro or chloro compounds, NO.sub.3.sup.- and Cl.sup.-.
Accordingly, when oxidizable compounds are present in relatively low concentrations, less than 10,000 ppm, the water may be treated by the addition of one or more oxidizing agents accompanied, in some instances, with irradiation. Oxidizing agents which result in the production of hydroxyl and hydroperoxy radicals are typically employed. These radicals are very strong oxidizing agents and, in addition, they indiscriminately oxidize all organic compounds. Typical sources of such oxidizing radicals are ozone and hydrogen peroxide. The irradiation is normally conducted by using ultraviolet light having a wave length of from about 200 to about 300 nm. The choice of oxidizing agent and the use of ultraviolet light will depend upon various factors including the concentration of oxidizable contaminants in the water stream, the required amount of oxidizing radical and the pH of the water.
The oxidation/photooxidation treatment may be conducted to any stage of completion which is required. If the only contaminants present in the water are oxidizable contaminants, the water may be treated so that it meets environmental requirements for use or disposal. Alternatively, the water may be recycled or, if other non-oxidizable contaminants are present, subjected to further treatment.
Typically, waters can be held in holding tanks prior to the oxidation/photooxidation treatment. In such cases, the water is exposed to carbon dioxide. As a result of this exposure, carbonate and bicarbonate ions are formed. These ions compete for the oxidizing hydroxyl radicals. As a result of this competition, the amount of oxidizing agents to be added to the solution may have to be increased if the treatment rate is not to be greatly diminished. However, if ozone is being used, then it may not be possible to increase the flow rate of ozone to the oxidation reaction without increasing the size of the ozone plant. There is therefore a need for an efficient method to control the competition for the oxidizing radicals by the carbonate and bicarbonate ions.